Periodic Trends

Trends on the periodic table

atomic radius

half the distance between the nuclei of two adjacent atoms of the same element

atomic radius: down a group

radius increases - more energy levels create a larger radius

atomic radius: across a period

radius decreases - there are more protons and no new energy levels (Zeffective is greater) so the radius shrinks

shielding effect

decrease in the attraction of the valence electrons towards the protons due to the presence of the energy levels between the nucleus and valence electrons

effective nuclear charge

the perceived attraction the electron has for the protons in the nucleus; the more shells there are, the weaker the Zeffective becomes b/c the protons are attracted to the electrons closest to the nucleus

Ionization energy

amount of energy required to remove one valence electron form an atom and form a +1 ion

ionization energy: down a group

energy decreases - Zeff is weaker due to more shielding, so the electrons require less energy to remove

ionization enery: across a period

energy increases - same energy level but more protons so Zeff is greater and the electron is harder to remove

ionization energy: exceptions

Group 13, Group 16

group 13 exception

removing the last valence electron is easier then it should be because the full "s" sub level acts as a mini shield

group 16 exception

due to electron repulsion, the 4th "p" electron is easier to remove

second ionization energy

the amount of energy needed to remove the second (third,fourth,etc) valence electron from an atom increases

electronegativity

the attraction an element has for the electrons in a chemical bond

chemical bond

two electrons that are linking two atoms together

electronegativity: down a group

electronegativity decreases - the more energy levels, the greater the shielding effect = the lower attraction for electrons

electronegativity: across a period

electronegativity increases - there are more protons, so the shields stay the same and the Zeff is greater causing more electrons to be attracted to the nucleus

electron affinity

the energy that is lost when an atom gains an electron - forms an anion; any time an attraction/bond is formed, energy is released;any time an attraction/bond is broken energy is gained

electron affinity: down a group

electron affinity decreases - the increase in electron shields decreases the atoms ability to attract electrons

electron affinity: across a period

electron affinity increases - it gains protons but the number of energy levels remains the same (the Zeff increases), so there is a greater attraction for electrons

electron affinity: exceptions

group 2,15,18

group 2 exception

"s" sublevel is full, so when it gains an electron, you need to add to the "p" sub level which is further away from the nucleus

group 15 exception

all "p" sublevels are half way full, so another electron will experience electron repulsion, decreasing the attraction

group 18 exception

the valence shell is full so there's no room for another electron